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CATEGORIES:BPI Seminar Series
SUMMARY:Experimental modelling of the Fluid Dynamics of Ma
gma Chambers / Buoyancy induced Taylor dispersion
- Andrew Gilbert\, BP Institute / Tiras Lin\, BP I
nstitute
DTSTART;TZID=Europe/London:20140619T113000
DTEND;TZID=Europe/London:20140619T123000
UID:TALK52904AThttp://talks.cam.ac.uk
URL:http://talks.cam.ac.uk/talk/index/52904
DESCRIPTION:Experimental modelling of the Fluid Dynamics of Ma
gma Chambers \n\nDetermining whether magma chamber
s convect is of importance for volcanologists and
geologists alike. The reason why some solidify to
form plutons and others erupt is still uncertain.
This study has done mathematical and experimental
modeling of a simple analogue basaltic magma chamb
er to determine the conditions under which convect
ion occurs. The experimental set up used is a tank
heated from below and cooled from above\, separat
ed into porous and fluid layers with thermal and i
mage data taken. Various regimes are possible\, in
cluding regimes in which the particles forming the
porous layer become entrained into the convecting
fluid. Textural analysis of plagioclase aspect ra
tios in igneous bodies has also been done to deter
mine the solidification histories of various igneo
us intrusions. \n\nBuoyancy induced Taylor dispers
ion\n\nWe consider the turbulent mixing that occur
s due to the injection of a small constant volume
flux of dyed salty fluid at the top of a long narr
ow tank tilted at an angle from the vertical. Usin
g dye and a light attenuation technique\, the evol
ution of the reduced gravity can be extracted thro
ughout the tank\, which is initially filled with f
luid of lighter density. The injected fluid mixes
vigorously with the fluid that initially occupies
the tank\, and a mixed region of turbulent fluid s
lowly propagates through the tank due to the unsta
ble density gradient that is set up along the leng
th of the tank. The evolution of the mixing region
along the length of the tank can be described as
a diffusive process using Prandtlâ€™s mixing length
theory\; the tilt causes a shear flow that enhance
s the effective diffusion\, in a way analogous to
Taylor dispersion for turbulent pipe flow. We show
that the solutions to the corresponding nonlinear
turbulent diffusion equation match well with our
experimental profiles throughout the range of tilt
angles tested (0-45 deg.)\, and that the profiles
of reduced gravity along the length of the tank t
ake on a self-similar form. Across the width of th
e tilted tank\, a density gradient is formed throu
ghout the mixed region of dense fluid\; we develop
a model for the cross-tank profiles of velocity a
nd reduced gravity based on the Navier Stokes equa
tion and the advection-diffusion equation\, and sh
ow good agreement between our model and our experi
mental data.
LOCATION:Open Plan Area\, BP Institute\, Madingley Rise CB3
0EZ
CONTACT:Catherine Pearson
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